Growth in the video camera industry as a whole has been fueled by decades of innovation and dramatic increases in integration and reduced costs of video cameras and their subsystems. For example, charge-coupled device (CCD) and CMOS imaging chips now offer mega-pixel resolution. In addition, very recent advances in imaging techniques and deblurring algorithms offer video recording with vibration immunity.
Due to their ever decreasing costs and increasing performance, video cameras now play an almost ubiquitous roll in all levels of society. In the business world, applications of close circuit cameras include video conferencing and security. In law enforcement, video cameras are indispensable surveillance and reconnaissance tools. In the consumer market, camcorders, camera phones, and webcams are fast becoming commonplace household items.
Given the market trends towards miniaturization and integration, it may seem somewhat surprising that pan and tilt functions of small form factor remotely controlled video cameras still rely on traditional slow-moving motor gear technologies. Pan/tilt video cameras, which represent a subset of the video camera market that is particularly relevant to the present invention includes, include a pan/tilt mechanism that allows automated panning and tilting of the camera angle during operation, thereby allowing a user to remotely control the captured image by remotely “aiming” the camera in substantially any direction. Pan/tilt mechanisms typically include a tilt motor for controlling the camera's tilt angle (i.e., the angle of the camera's “aiming” direction relative to a horizontal plane), and a separate pan motor for controlling the camera's pan angle (i.e., the rotational direction of the camera's “aiming” direction relative to a vertical axis).
The most common miniaturized pan/tilt camera systems, commonly referred to as domed PTZ (for pan-tilt-zoom) cameras, use a motor-on-motor gimbal mounting pan/tilt mechanism having a complicated gear train and a domed shaped protective cover. A problem with conventional PTZ cameras is that both the camera (i.e., including the lens and image capturing device) and the tilt motor are supported on a rotating platform driven by the pan motor. The overall size of a typical conventional PZT video camera system is still several inches in diameter. One possible reason such systems have not been miniaturized further is that the pan and tilt angle requirements are quit large (typically greater than 180 degrees of panning and greater than +/−45 degrees of tilt). In addition, because the entire camera must be moved by the tilt motor, and both the camera and tilt motor must be moved by the pan motor, the motional mass of even the latest miniaturized stationary cameras in cell phones is quite large in comparison to the loads miniature technologies such as MEMS can traditionally move. The large mass reduces pan/tilt operating speeds, limit miniaturization of the pan motor, and can introduce cross axis tracking errors due to the motor-on-motor gimbal structure of the PZT pan/tilt mechanism.
Several approaches have been proposed to reduce the mass of pan/tilt mechanism in order to facilitate miniaturization. One approach is to move the camera off of the rotating platform of the pan/tilt mechanism, which involves mounting a lighter weight mirror that is controlled by the tilt motor on the rotating platform, and controlling a tilt angle of the mirror to redirect light to the camera, which is mounted nearby. While this approach reduces the weight supported on the rotating platform, it still requires that the tilt mechanism (i.e., a tilt motor arranged to pivot the mirror) be mounted on the rotating platform, thus limiting miniaturization and operating speed improvement. The weight issue may be addressed by constructing the mirror on a Micro-Electro-Mechanical Systems (MEMS) device, but such MEMS devices typically have a limited range of motion and require a constant power draw in order to maintain a selected tilt position.
To summarize the current state of pan/tilt mechanism technology, the main advantage of the macroscopic motor based pan-tilt mechanisms is that the pan and tilt position can be positioned and maintained using simple pulse driven DC motors or a stepper motors with little or no power draw in a hold position. A large image can be taken at once without having to build up a larger field of view. The main advantage of a MEMS based approach is a compact and possibly lower cost design. However MEMS systems usually require constant power draw so they are not useful for autonomous or remote wireless applications.
What is needed is a low cost pan/tilt actuation platform for use with portable and stationary video camera devices that avoids the problems associated with the various conventional pan/tilt mechanisms described above. In particular, what is needed is a micro mirror-based miniature pan/tilt system that can achieve high bandwidths and a wide range of pan and tilt motion with ideally low current draw in a hold state.